(Meth)acrylate ammonium salts and their use as monomers for the synthesis of polymers useful as flocculants have been described in WO 01/55088, WO 01/55089, WO 01/55225 and US2002/0035198. In these publications the (meth)acrylate ammonium salts are synthesised by the reaction of the corresponding di-amine (meth)acrylate with less than 2 equivalents of an alkyl or a benzylhalide in an organic solvent such as chloroform and with the addition of water to remove the produced (meth)acrylate ammonium salt. EP 1 253 137 describes a synthesis were the organic solvent is an acrylate ammonium salt. Again, near the end of the reaction period, water is added to remove the produced salt. These processes yield aqueous solutions of a mixture of a (meth)acrylate di-ammonium salt and a (meth)acrylate mono-ammonium salt. These processes do not permit to isolate (meth)acrylate di-ammonium salts with a high purity. It is also almost impossible to purify the obtained mixtures. When used as monomers in the synthesis of polymers, these polymers will inevitably contain a significant amount of units derived from the mono-ammonium salts. In order to effectively build-in double charged monomers into polymers, the (meth)acrylate di-ammonium salts need to be obtained selectively. In order to be useful as starting material for the production of high molecular weight polymers and copolymers for flocculation, the di-ammonium salts need to be very pure.